Boundary Stress
The Boundary Stress node adds a boundary condition that represents a general class of conditions also known as traction boundary conditions.
Boundary Condition
The Boundary condition options for the boundary stress are General stress, Normal stress, and Normal stress, normal flow.
General Stress
When General stress is selected, the components for the Stress F should be specified. The total stress on the boundary is set equal to the given stress F:
for the compressible and the incompressible formulations.
This boundary condition implicitly sets a constraint on the pressure that for 2D flows is
(4-6)
If ∂un/∂n is small, Equation 4-6 states that p ≈ −n·F.
Normal Stress
Normal Stress is described for the Open Boundary node.
Normal Stress, Normal Flow
For Normal stress, normal flow, the magnitude of the Normal stress f0 should be specified. The tangential velocity is set to zero on the boundary:
for the compressible and the incompressible formulations.
This boundary condition implicitly sets a constraint on the pressure that for 2D flows is
(4-7)
If ∂un/∂n is small, Equation 4-7 states that p ≈ f0.
When Include gravity is selected and Use reduced pressure not selected in the interface Physical model section, the Compensate for hydrostatic pressure approximation (named Compensate for hydrostatic pressure for compressible flows) check box is available and selected by default. When it is selected, the hydrostatic pressure is automatically added to the pressure entered in f0 or phydron is added to F depending of the selected option.
Turbulent Boundary Type
The Turbulent boundary type options for this boundary condition are Open boundary, Inlet, and Outlet.
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For Open boundary parts of the boundary are expected to be outlets and other parts are expected to be to be inlets.
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The Inlet option should be selected when the whole boundary is expected to be an inlet.
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The Outlet option should be used when the whole boundary is expected to be an outflow boundary. In this case, homogeneous Neumann conditions are applied for the turbulence variables, that is, for k and ε
and additionally for the v2-f model
for k and ω
or for the Spalart-Allmaras model
Turbulence Conditions
See Turbulent Flow Settings.
Constraint Settings
This section is displayed by clicking the Show button () and selecting Advanced Physics Options.
If Normal Stress, Normal Flow is selected as the Boundary condition, then to Apply reaction terms on all dependent variables, the All physics (symmetric) option should be selected. Alternatively, the Individual dependent variables could be selected to restrict the reaction terms as needed.